1. Field of the Invention
The present invention relates to light emitting waveguides such light pipes, optical fibers or planar waveguides provided with a series of optical elements distributed along the optical path to provide for a controlled illumination pattern. This invention also relates to optical illuminators and light distribution systems employing such waveguides, for example, side-emitting optical fibers, panel luminaires, edge-lit LED backlights and lighting panels, LCD display backlights, computer screens, advertising displays, road signs, and the like, as well as to a method for redistributing light from a variety of light sources.
2. Description of Background Art
Conventionally, illumination systems incorporating optical waveguides use the Total Internal Reflection (TIR) as the means for light propagation through the waveguide which is usually made from a transparent dielectric material. The waveguides comprise a core, commonly of an inorganic glass or polymeric plastic material, which can be surrounded by air in which case the light propagation by means of TIR can occur for the broadest range of propagation angles for a given core material. Alternatively, the waveguide may further incorporate a cladding layer that has a lower refractive index than the waveguide material in order to maintain the TIR properties for the core. This provides protection of the core from the environment, but also usually narrows the range of propagation angles compared to the optical interface formed by the waveguide's core with air.
The side-emitting optical fibers are usually illuminated from one or both terminal ends and have a series of some sort of light reflecting or scattering elements distributed along the fiber and causing portions of the light propagating in the fiber to leak outside at the controlled locations so that the light can be uniformly emitted along the entire length of the fiber.
The planar waveguides of edge-lit backlighting panels and luminaires can be illuminated from one or up to four its edges, which is conventionally done using individual LED's or LED strips. The light reflective or scattering elements are usually distributed along the planar surface opposite to the light emitting surface according to a predefined pattern in order to obtain a uniform surface brightness.
However, these prior art devices usually lack the collimating ability as the light outcoupled from the waveguide by the reflectors or scattering elements emerges from the waveguide highly divergent. This divergence is defined by the multitude of light propagation angles in the waveguide and by the properties of the reflectors. In many applications, however, an improved collimation can be required, for example, in order to increase the lighting panel luminosity toward a given direction or improve the irradiance intensity on an object that the waveguide-based backlight is illuminating.
It is therefore an object of this invention to provide an improved illumination system employing a waveguide structure with efficient light outcoupling and collimation that would enhance the energy efficiency and the utility of the device. The present invention solves the above problems by providing a portion of the waveguide that is shaped in the form of a linear collimating lens or a plurality of parallel collimating lens and by further providing a string of light-outcoupling optical reflectors disposed in proximity of the focal line of the collimating lens. As each reflector extracts a small portion of the light propagating in the waveguide from waveguide's longitudinal surface, the collimating lens intercepts and collimates the extracted light in at least one dimension, particularly in a plane perpendicular to the longitudinal axis of the waveguide or to the prevailing direction of light propagation in the waveguide. Other objects and advantages of this invention will be apparent to those skilled in the art from the following disclosure.